An eddy current separator (“ECS”) is a device that separates electroconductive materials from non-electroconductive materials. A conventional ECS typically includes at least two pulleys over which a conveyor belt runs. Material to be processed is fed onto the conveyor belt, which moves the material across a magnetic rotor of the ECS.
The magnetic rotor includes a pulley on which a series of axial rows of permanent magnet blocks are mounted. Each row includes magnet blocks that have the same polar orientation. The polar orientation alternates from row to row. The pulley is mounted on a shaft.
The magnetic rotor is enclosed in (but not attached to) a non-metallic shell which supports the conveyor belt. This allows the magnetic rotor to spin independently and at a much higher rate of speed than the non-metallic shell and the conveyor belt. The faster rotation of the alternate axial polarity rows relative to the speed of the conveyor belt makes the material conveyed to the magnetic rotor by the conveyor belt cross a variable magnetic field that creates a circulating electrical current or “eddy current” in any electroconductive elements in the material.
The eddy current produces a magnetic field that has a polarity that is the same as the polarity of the magnet(s) that induced the eddy current. Since like magnetic poles repel on another, the material in which the eddy current is created is repelled and projected away from the conveyor belt along a predictable trajectory. The projected material is collected in a first receptacle disposed at the end of the trajectory. The non-electroconductive material falls from the end of the conveyor belt into a second receptacle. Thus, the magnetic rotor separates the electroconductive and non-electroconductive materials into the first and second receptacles, respectively.
ECS's are used in many different industrial and non-industrial applications. For example, an ECS may be used to separate and recover like materials in a waste stream. Recycling of waste materials is highly desirable from many viewpoints, not the least of which are financial and ecological. Properly sorted recyclable materials can often be sold for significant revenue. Many of the more valuable recyclable materials do not biodegrade within a short period. Recycling of those materials significantly reduces the strain on local landfills and, ultimately, the environment.
Typically, waste streams are composed of a variety of types of waste materials. One such waste stream is generated from the recovery and recycling of automobiles or other large machinery and appliances. For example, at the end of its useful life, an automobile is shredded. The shredded material is processed to recover ferrous and non-ferrous metals. The remaining materials that are not recovered are referred to as automobile shredder residue (“ASR”). The ASR, which may still include ferrous and non-ferrous metals, including copper wire and other recyclable materials, is typically disposed of in a landfill.
Recently, efforts have been made to further recover materials, such as plastics and copper and other non-ferrous metals, from ASR. Similar efforts have been made to recover materials from whitegood shredder residue (WSR), which includes the waste materials left over after recovering ferrous metals from shredded machinery or large appliances. Other waste streams that have recoverable materials include electronic components (also known as “e-waste” or “waste electrical and electronic equipment” (“WEEE”)), building components, retrieved landfill material, municipal waste, either incinerated or not, and other industrial waste streams.
Many materials processed using ECS devices, including typical waste streams, include a variety of different electroconductive and non-electroconductive materials having diameters less than about 10 mm. For simplicity, such materials are referred to herein as “fines.” The ability of an ECS to separate fines effectively depends on the frequency of the ECS. Generally, the higher the frequency, the greater the ability of the ECS to separate fines effectively.
Increasing the frequency of a conventional ECS is problematic because the increased speed of the magnetic rotor can cause mechanical stresses on the ECS. For example, the mechanical holding force of the magnetic rotor of the ECS can be challenged by stronger centrifugal forces resulting from the higher speed of the magnetic rotor. In addition, the shaft of the magnetic rotor generally reaches its own natural frequency at about 5,400 rotations per minute. To ensure that the shaft stays sufficiently below its own natural frequency and to prevent the shaft from having resonance and harmonic problems that the ECS would not be able to withstand, a speed limit of approximately 3,000 rotations per minute for an ECS up to 1.5 meters wide to 4,000 rotations per minute for an ECS up to one meter wide generally has been imposed.
Therefore, a need exists for an ECS that can effectively separate fines. In particular, a need exists for an ECS that can durably operate at a high frequency.